Thanks again, Randy, for helping me out of this mess.
I begin to know how to edit in piano roll, but I don't se any CC in there, unless I op one or more lanes under the piano roll. They don't show however to which CC they're attached. I assume volume will be CC7 and expression is CC11 (as one could expect). I'll try do do exactly as you say. If it doesn't work, I can always discard the attempt.
BUT - All of what's going on in this project file will be clear to you, Max, if you start understanding how to use whatever Logic calls its Piano Roll View. That's the heart of MIDI for all DAW programs. You can have all data in a file displayed, and you can edit it. For this file you're working on, you would open it, and I guarantee you will see lots of CC7 data - that's what's making your sliders jump. As long as that data is in there, your sliders will be controlled by the data. So, either erase it as Jeff suggests, or look to see if you have proper instrument volume control in a CC11 Expression lane. If you have no data there, paste the CC7 into it. If you do - leave it, and erase the CC7.